Non-typeable Haemophilus influenzae are non-encapsulated organisms that are defined by their lack of reactivity with antisera against known H. influenzae capsular antigens.
These organisms commonly inhabit the upper respiratory tract of humans and are frequently responsible for a variety of common mucosal surface infections, such as otitis media, sinusitis, conjunctivitis, chronic bronchitis and pneumonia. Otitis media remains an important health problem for children and most children have had at least one episode of otitis by their third birthday and approximately one-third of children have had three or more episodes. Non-typeable Haemophilus influenzae generally accounts for about 20 to 25% of acute otitis media and for a larger percentage of cases of chronic otitis media with effusion.
A critical first step in the pathogenesis of these infections is colonization of the respiratory tract mucosa. Bacterial surface molecules which mediate adherence, therefore, are of particular interest as possible vaccine candidates.
Since the non-typeable organisms do not have a polysaccharide capsule, they are not controlled by the present Haemophilus influenzae type b (Hib) vaccines, which are directed towards Hib bacterial capsular polysaccharides. The non-typeable strains, however, do produce surface antigens that can elicit bactericidal antibodies. Two of the major outer membrane proteins, P2 and P6, have been identified as targets of human serum bactericidal activity. However, it has been shown that the P2 protein sequence is variable, in particular in the non-typeable Haemophilus strains. Thus, a P2-based vaccine would not protect against all strains of the organism.
There have previously been identified by Barenkamp et al (Pediatr. Infect. Dis. J., 9:333-339, 1990) a group of high-molecular-weight (HMW) proteins of non-typeable Haemophilus influenzae that appeared to be major targets of antibodies present in human convalescent sera. Examination of a series of middle ear isolates revealed the presence of one or two such proteins in most strains. However, prior to the present invention, the structures of these proteins and their encoding nucleic acid sequences were unknown as were pure isolates of such proteins. In addition, the identification of surface accessible epitopes of such proteins was unknown.